1. Field of the Invention
The present invention relates to a traffic monitoring apparatus for monitoring the number of objects such as people moving past an area under surveillance such as, for example, entrance and exit portals of a revolving door.
2. Description of the Prior Art
In recent years, as a security technology to curb the flow of information from corporations, the control system is known, in which a verifying device is installed in each of the important entrance and exit of a commercial building so that only when a person is attested as an authorized person through the ID card or the fingerprint, the door at the entrance or exit can be opened.
With the foregoing security technology, it is necessary to block passage of one or more persons trying to pass through the entrance or exit while tailgating, or following side by side with, the authorized person, who has been given a permission to pass through the entrance or exit after having inserted his or her regular ID card into an ID card verifying device. Accordingly, attempts have hitherto been made to lay a body weight sensitive floor mat on an area under surveillance in the vicinity of the door so that when the body weight detected by the body weight sensor built in the floor mat is greater than a threshold value, determination can be made that a plurality of persons exist and the opening of the door is hence inhibited and, alternatively, to use a monitoring system in which a plurality of ultrasonic sensors are secured to the ceiling above the door, with those ultrasonic sensors storing on a time-series basis information on the body height of an object measured thereby, so that when the average body height of a person appears continuously in the body height information, determination is made that there are two persons and the opening of the door is hence inhibited. See, for example, U.S. Pat. No. 5,201,906.
On the other hand, as another monitoring device, it is known to use a method in which a contour pattern in image data imaged with a tracking camera installed at the area under surveillance in the vicinity of the door is compared and collated with a reference pattern stored beforehand to determine the number of persons existing. See, for example, Published United States Patent Application No. 2004/0017929.
It has, however, been that with the monitoring device in which the body weight sensitive floor mat is laid, and considering that it may occur that the body weight of a single person of a big build would exceed the sum of respective body weights of two persons of a small build, setting of the threshold value to a low value will result in that an authorized person of a big build will not be allowed to pass, but setting of the threshold value to a high value will result in that two persons of a small build will be allowed to pass. Also, with the monitoring device in which the ultrasonic sensors are installed, when two persons in proximity to each other try to pass, information will become comparable to the body height information on a single person on a time-series basis, resulting in an erroneous determination that it is a single person. On the other hand, with the monitoring device based on the image data photo-taken by the tracking camera, the pattern matching cannot be taken, resulting in an erroneous determination in the event that a plurality of persons try to pass in a posture not found in the preset reference pattern, for example, in the event that one person in a standing posture and another person in a bowing posture try to pass.